Concentration of ores



Patented Feb. 1, 1938 UNITED STATES PATENT OFFICE Pacific Palisades, Tacoma, Wash.

Calif., and Earl F. Hailey,

No Drawing. Application October 21, 1936, serial No. 106.800

6 Claims.

This invention relates to the concentration of ores, minerals and the like by the flotation process, and more particularly to those ores containing oxidized minerals and those known as non-metallic ores.

One of the objects of this invention is to provide an improved method in froth flotation, in which a reagent or combination of reagents used will render the operation more selective by de- 10 pressing, retarding or preventing the flotation of the undesired or objectionable material, thus obtaining a richer concentrate of the desired mineral and in many cases at the same time more of the desired mineral.

Another object of the invention is to provide a method of this type, wherein the reagents used not only will depress or retard flotation of undesired material, but also will have the effect of increasing the floatability of the desired products.

We have discovered that a solution containing a soluble cyanide, preferably an alkaline or alkaline earth cyanide in combination with fatty acids of high molecular weight and salts thereof, for example, oleic acid or sodium oleate, used as collecting agents, produce a more selective action in effecting the flotation of desired materials. The concentrates produced contain a superior grade of the desired mineral and in many cases the mineral to be floated is also activated, thereby giving a larger quantity of concentrate 3 without diminution of grade.

This invention is based upon the discovery that cyanide, when used in flotation, is a selective depressor of silica and of silicious gangue material, when used in combination with oleic acid as a collector, or fatty acid analogues of oleic acid, normally used as flotation collectors for oxidized or non-metallic minerals.

Oleic acid has long been known to have superior ability to be adsorbed by particles to be floated and thus to function as a collector, when used in flotation work, but it has the disadvantage of exhibiting little selectivity. That is, it will float not only what is wanted, but also what is unwanted. Efforts have been made to improve or to control its selectivity, such as by adding sodium silicate thereto, but so far without success. So a paramount factor of this invention is the teaching that the selectivity of oleic acid or its fatty acid analogues used as a collector with frothing agents in flotation, can be refined and controlled by the use in association therewith of cyanide by virtue of which the ability of the oleic acids collecting functions is inhibitedwith respect to silica and silicious gangue materials. Indeed it may be that the prime importance of the teaching of this invention is that cyanide, when used in an ore mixture in a flotation cell. has an inhibiting action upon the flotation of silica and other gangue.

Heretofore when employing oleic acid or soaps in the flotation of ores and minerals, the objectionable feature has been the amount of silica and other gangue minerals in the froth, and therefore in the concentrate. This causes a low grade concentrate, and close control of the amount of soap is required in order to make a marketable product. The use of depressors or deactivators such as sodium silicate, gums, etc., for silica or other gangue depression, has in many cases been attended by depression of the mineral to be floated. In many cases, unless the amount of these depressants is closely controlled, they themselves may reactivate the silica and gangue when greater than the optimum amount is used. I

The essence of this discovery is an improvement in the flotation of ores and minerals by soaps in the presence of a soluble cyanide, which is believed to act as a modifying agent.

We have discovered that when using a soluble cyanide in combination with high-molecular weight fatty acids or their salts, an elimination of silica and other gangue material takes place and an excess over and above the optimum amount does not materially effect an increase in silica or gangue mineral in the froth, whereas an increase in other commonly used modifying reagents such as caustic alkali, sodium silicate, etc., over and above the optimum amounts often tends to give inferior results. The use of an increased amount of cyanide above the optimum amount does not, however, alter the results to the same extent. This characteristic permits a greater latitude of control. While some depression of the desired mineral has at times been encountered when using large amounts of cyanide, it has not been serious, the silica and gangue not having been reactivated.

In soap flotation pH control is of great importance and an optimum pH is also of benefit when flotation is practiced with the use of cyanide.

As an illustration of the effects of cyanide in comparison to other reagents upon quartz activated by copper sulphate, using oleic acid as the collector and pine oil as a frother, the following comparative tests are cited:

Percent Test No. Modifying agent Hi0,

, floated 780 N 28 790 0.4 lb NaON er ton. 7. 2 791 4 lb Na'CO per ton. 48

This same effect is noticeable in the flotation of kyanite (AhOsSlOz), a non-metallic mineral,

In the above-mentioned cases no apparent activation of the desired mineral to be floated is noticed, however, as stated heretofore, some minerals appear to be activated and at the same time a depression or retarding of the silica and other gangue material is .efi'ected. The following case is an example of results obtained on an African copper ore. Concentrate analysis only given:

Percent Percent Extrac- Test Modiiyingreagent tot. cu. ox. cu. tions Percent No. present coneonpercent ex. on.

tained tained tot. cu.

706 10 lbs. ton lbacNfuflgu 82. 9 2i. 9 76. 4 67. 5 707 4 r 11 The above examples are illustrative and typi cal of the many minerals to which this invention may be applied.

Another noticeable property of the use of cyanide is its effect upon the character of the froth produced. Frequently in order to obtain an economical extraction of certain ore and minerals comparatively large amounts of collecting,

agents, such as oleic acid, must, be employed. This results in a very heavy, stifl', gummy" froth and the addition of cyanide has the effect of correcting this gummy condition and affords a commercial froth as known in the flotation art.

Another noticeable feature of the effect of cyanide is its action in the presence of slime material. It is known :that deslimed material-can often be concentrated by means of soaps and fatty acids. However, since even the utmost care in grinding does not eliminate the production of some slime in the pulp, and these slimes often carry valuable mineral to be floated, their extraction is pertinent to successful flotation practice. As an illustration, we cite the effect of cyanide on the deslimed and slime portion of an African copper ore:

While no particular mention has been'made of the efl'ect of cyanide on the recovery of sulphide mineral when present with oxide mineral in the pulp, the following is given as a concrete example:

Percent Pa Extraction Test cent No. total Modi- M l reagent Percent Percent 1pm d 6 phide Percent on. total on.

oxide on.

NaCN None In the example above cited, the sulphides and oxides were both floated together without preliminary removal of sulphides before floating the oxides. This one step flotation is of considerable advantage in that it is not necessary to remove the sulphides before the oxides may be successfully floated. However, should it be of advantage from a subsequent concentrate treatment standpoint, the sulphides may be floated by known methods before activating and floating the. oxides, as a second step.

As an example as to the ways our invention may be practiced, the ore is first ground to detach the mineral particles from the gangue or silica. Liberation of the mineral particles within the economic limits-of the subsequent step of flota. tion, only is sought. This operation is conducted in water and the pulp is then subsequently sub- Jected to the froth flotation process. The reagents all or part may be added tothe grinding operation or may be added all or part to the flotation operation. Our best results have been obtained by adding the fatty acid and the cyanide to the grinding circuit subsequently adding a frothing agent and/or other additional collecting agents such as xanthate to the flotation circuit. On some ores the subsequent addition of xanthate and pine oil has been done in stages, with improved results.

The term salts of fatty acids is not to be limited to only those salts which are soluble, for, insofar as we know, the insoluble salts may work just as efliciently. For example, a test was made wherein ordinary tap or hard water wasused, and another test in which distilled water was used giving the following results:

M Oxide No. Water Reagent wi Oxide ex-' grade traction Tap (hard)..-. Distilled.

Distilled NaOleate NaCN NaOleate NaCN..'.. NaOleatel of adding such insoluble soaps to the ore pulp to bring about maximum dispersion in order for them to function the same as soluble soaps.

The specific process above described is given only by way of example and many modifications may be made therein without departing from the spirit of our invention. For instance. the proportions and type of frothing agents used may be varied; other assisting and" collecting agents such as the xanthates may be used; alkalinity may be varied; these all depending upon the type and character of the ore. The amount of cyanide and soap to be'used has been found to be a function of the speciflc ore to be treated. Cyanide amounts have been found so far'to vary from .05 lb. per ton to 3 lb. per ton. The same is true of the soap or fatty acid amounts which ranged from .25 lb. per ton to 4 lb. per ton.

The process of the present invention is particularly applicable in selective flotation operations to separate oxides of copper from ores containing the same. sulphide minerals such as sphalerite and pyrite have heretofore been satisfactorily separated from their ores and each other by the use of well known collecting agents. principally xanthates.

In such cases separation of the desired minerals from the gangue is not particularly difficult because of the fact that the xanthates and other collectors used do not tend to float silica and silicious gangue. The xanthates and other collectors of sulphide minerals, however, will not float the oxide minerals in a satisfactory and commercial manner. The fatty acids and salts thereof have been found to be excellent collectors for the oxide minerals and will float them readily in large quantities.

The problem met with, however, is that these fatty acids exhibit no selectivity and will float large quantities of silica and siliclous gangue along with the desired mineral. So-called depressors of silicious gangue, such as sodium silicate, sodium carbonate, etc., appear to exert more of a dispersing action, and our experiments show that this is insufficient in the case of oxidized copper ores and kyanite. We have made tests in which the ores have been dispersed with sodium silicate and floated with oleic acid, and the results were unsatisfactory. The use of cyanide instead of the sodium silicate gave high grades of concentrates and generally superior results. Therefore, our, invention makes use of the discovery that the combination of a fatty acid and a soluble cyanide effects the obtaining of a high grade concentrate rich in oxidized mineral values. and at the same time prevents or inhibits the flotation of silica and silicious gangue, thereby effecting a clean separation and a recovery of oxidized values such-as has not been commercially satisfactory heretofore.

V In the appended claims the term fatty acid is intended to cover the fatty acids of high moiecu lar weight .and the salts thereof such as oleic acid or oleates, stearic acid or steal-ates, etc. The term soluble cyanide as used herein refers to any cyanide which is soluble to the extent to which it is added to the ore and water mixture. Wherever in the appended claims the term silicateoxide ores" is used, this term is intended to designate and embrace any ore which has among its component constituents an oxidized mineral which is amenable to flotation and a gangue containing silicious material.

The term, desired mineral, used herein does not necessarily describe the valuable constituent of the ore to be treated. For exampiethe valuable constituent of glass sand is found in the tailings after floatabie materials have been floated off. In this case the desired mineral designates the floatable' impurities while the valuable constituen is that portion not found in the froth.

We claim:

1. The process of concentrating oxidized ores containing silicious gangue material which comprises adding to the ore pulp a fatty acid or salt thereof to act as a collecting agent and a soluble cyanide to act as a depressing agent for silica and other gangue and subjecting the pulp to froth flotation.

2. The process of concentrating ores containing oxidized minerals and silicious gangue material,

which comprises adding to the ore pulp a. fatty acid or salt thereof to act as a collecting agent for the oxidized minerals, adding a soluble cyanide to' act as a depressing agent for gangue material, and subjecting the pulp to froth flotation to obtain a concentrate containing the oxidized min erals.

3. The process of concentrating silicate-oxide ores which comprises adding to the ore pulp oleic acid or an oleate and a soluble cyanide, and subje'cting the pulp to froth flotation.

4. The process of concentrating silicate-oxide ores which comprises adding to the ore pulp, stearic acid or a stearate and a soluble cyanide and subiecting the pulp to froth flotation.

6. The process of concentrating silicate-oxide oreswhich comprises grinding the ore together with a fatty acid and a soluble cyanide and sub- .iecting the resulting pulp to froth flotation.

6. In the concentrating of silicate-oxide ores by froth flotation, the method which comprises 

